i'm bob abernethy. you can follow us on twitter and facebook and watch us anytime on the pbs app for iphones and ipads. there's always much more on our web site as well, including a list of some organizaons at offer alternative gift ideas. you can comment on all of our stories and share them. audio and video podcasts are also available. join us at pbs.org. as we leave you, scenes from paris where celebrations were held to mark the 850th anniversary of the cathedral of notre dame .